A great number of industrial reactions are conducted in mixing-chamber type reaction apparatus wherein a solid catalyst is made into a slurry and used. The catalyst made into the slurry is made of fine powder. In the presence of the catalyst, a reactive gas such as hydrogen or ammonia is brought into contact with a liquid to conduct reaction. When the reaction ends, the catalyst is generally removed by filtration, so as to collect the reaction product.
However, a catalyst in a slurry form has problems about safety, an increase in wastes, operability, productivity and so on. For example, one of the problems is a problem that many catalysts are naturally ignitable, thereby causing an anxiety about safety. A second one thereof is a problem that the catalyst generally needs to be removed by filtration in order to collect a reaction product, thereby making facilities therefor and the operation thereof complicated.
An example of a production process which neither needs any mixing operation, such as stirring or gas bubbling, nor any separation of a catalyst by filtration is a fixed bed process. As the catalyst used in the fixed bed process, there have been hitherto well-known molded catalysts such as pellet-form, noodle-form or tablet-form catalysts. The catalysts are each a catalyst wherein a powdery material having catalyst activity is molded into any one of the above-mentioned forms by compression, extrusion or some other method, thereby forming a structure having therein countless pores so as to make the form of bulk compatible with a high surface area. The process is disclosed in, for example, JP-A-6-211754.
As a different method for fixing a catalyst, known is a method of forming a thin catalyst layer in a film form inside a reaction field. For example, JP-A-2003-176255 discloses a reactor wherein a catalyst metal is caused to adhere onto the surface of a monolith. Therein, the following advantage is indicated: in a hydrogenating reaction between a reactant gas and a reactant liquid, a drop in the pressure inside the reactor is small so that speeds of the gas and the liquid can be made large; therefore, the mass transfer therein is further promoted than in fixed bed filled reactors of conventional types.
A different reactor using a monolith catalyst is disclosed in JP-A-2003-275577. In order to improve the solubility of a reactant gas into a reactant liquid, the gas is finely dispersed by the rotation of a turbine impeller fitted onto a housing into which the catalyst is put, and in order to control the convection state of the reactant liquid, a baffle is used. In this way, the selectivity of a hydrogenation reaction for producing aniline from nitrobenzene is improved.